161
FXUS61 KPBZ 101010
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
510 AM EST Fri Jan 10 2025

.SYNOPSIS...
Dry and cold today. Snow, associated with a storm system over
the southeastern US, will begin to overspread the region late
today and continue into Saturday. More lake enhanced snow
showers are possible later Saturday and Saturday night. Dry on
Sunday before more cold and snow chances return next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
KEY MESSAGES:

- Most of the day will be snow free.
- Clouds will increase from the west this afternoon.
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A weak ridge will pass quickly through the area this morning.
Rapid height falls are then expected this afternoon as the ridge
moves over New England and a deepening trough races across the
Midwest. Cirrus cloud will spread across the area this morning,
with mid clouds blanketing the region during the afternoon.

Still seeing some timing differences in how quickly snow will
begin to fall over western reaches of the forecast area. Would
think a slower progress would be appropriate as a very dry
atmosphere is resting over the region and it will take time to
moisten the lower levels.

Temperatures will again be well below normal.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
KEY MESSAGES:

- Snow tonight through Saturday morning area-wide.
- Snow showers possible later Saturday downstream of Lake Erie.
- Dry Sunday but still cold.
--------------------------------------------------------------------

The next trough axis will reach western Ohio late tonight and
then quickly swing through the Upper Ohio Valley Saturday
morning. Moisture associated with a deepening surface low moving
across the southeastern US will advect northward ahead of the
trough. Snow will spread westward across the area this evening,
and should cover the entire forecast area by midnight. With a
very cold atmosphere in place dry, fluffy, high ratio snow is
expected.

Widespread snow is anticipated into Saturday morning until the
trough axis swings eastward taking the upper level moisture with
it. Thereafter, a period of cold air advection and northwest
flow will begin Saturday afternoon. The setup for lake enhanced
snow is not optimal. With such a progressive pattern, upper
level height rises are expected late Saturday and a broad
surface high will move across Ohio. The cold air advection
Saturday afternoon is modest at best and forecast soundings are
showing the layer of saturation quickly dropping below the DGZ.
Even the latest CAM models are not displaying strong band
development. There should be lake enhanced snow showers Saturday
afternoon into Saturday night, but they may remain unorganized.

All in all, totals from the entire event appear to broadly be
in the 2" to 4" range with some higher totals in orographic
enhancement that has justified a winter weather advisory for the
ridges. Most of the synoptic snow will fall before sunrise on
Saturday.

Eastern Tucker will need watching, as an upgrade to a warning
may be possible if confidence in 6" increases. As for the rest
of the area not in an advisory, confidence remains too low at
this point for an upgrade with storm totals right around the
deterministic criteria. The highest probabilities of >3" remain
in northwest Pennsylvania and northeastern Ohio for now.

An upper level ridge and high pressure at the surface will keep
Sunday dry and cold. Decreasing cloud cover is possible Sunday
afternoon.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:


- Weak low pressure returns snow chances Monday.
- Periodic snow chances with below-normal temperatures favored next
  week.
--------------------------------------------------------------------

Another upper low looks to take shape well off to our north for
the start of next week. A de-amplifying wave on its southern
periphery is progged to slide through on its periphery late
Sunday into Monday as surface low pressure rides through the
Great Lakes. Snow chances may return as early as the first half
of the overnight Sunday night, but more likely the morning hours
of Monday. Moisture is not looking all that plentiful with
westerly low and mid-level flow, so this is looking more like a
light snow showers type event with potentially some low-end
accumulation in the ridges at the most. At the moment, chances
of >3" are 0% area-wide.

Headed into the rest of the week, ensembles all exhibit and
establishment of more zonal flow locally as upper troughing lingers
across the eastern seaboard. There`s uncertainty with how deep the
troughing will be, and thus how cold temperatures will get, but this
pattern is pointing toward below-normal temperatures continuing with
periodic snow chances tied to subtleties with embedded impulses in
the flow. The CPC`s 6-10 day temperature outlook is between a 60-80%
chance of below normal temperatures.

This long term cold signal maintains itself through the end of
the month. This will likely tend towards more ice coverage on
Lake Erie, and perhaps a reduction in lake-effect snow.
Additionally, more river ice appears likely, which may increase
risks of ice jams later this month. Continual cold temperatures
and cloudy weather will also maintain our snow pack and make
the area more susceptible to flooding when the next heavy
rainfall event occurs. Though these impacts are quite long-
range, they will warrant watching.

&&

.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
VFR conditions continue tonight at most ports, save DUJ where
ongoing MVFR lake-effect stratocu remains and MGW/LBE where
another shield of stratus has remained with shallow low-level
moisture. Moisture has been slow to erode at DUJ and
probabilities suggest that it may take until diurnal mixing
begins to erode the cloud deck. The evolution at LBE is lower
confidence as the moisture remains trapped and slowly spills
north. Again, it`s looking like we`ll need a similar mechanism
as further north but very light wind this morning will not help.

Otherwise, high clouds will thicken and lower throughout the
day ahead of the next approaching weather system, a trend that
is depicted in TAFs with sub-10kft cigs beginning mid to late
afternoon. Snow approaches from the west Friday evening, but
there is still notable discrepancy among the guidance on the
onset timing. At this point, have opted to err on the guidance
that is a bit later bringing steady snow to ZZV after 00z and
PIT after 03z as HREF soundings show low-level dry air that
will need to saturate before snow reaches the ground. Overnight
runs of the CAMs have begun to capture this drier trend. This
may result in a period of light snow initially but still high
end MVFR/low end VFR until saturation. Confidence in IFR
occurrence is on the high side at 80+% in SN, but confidence is
lower on the timing at this point and further refinements are
likely.

Winds remain light throughout the period, becoming variable
overnight and then predominantly out of the south or southeast
during the day Friday.

Outlook...
A cold NW flow pattern under broad upper troughing is expected
to remain through the weekend, allowing MVFR ceiling
restrictions and possibly some lingering lake-effect snow
showers to persist through Saturday night. VFR conditions are
expected to return on Sunday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory from 7 PM this evening to 1 AM EST
     Sunday for PAZ020-021-029-031-073>076-078.
OH...Winter Weather Advisory from 7 PM this evening to 1 AM EST
     Sunday for OHZ039>041-048>050-057>059-068-069.
WV...Winter Weather Advisory from 7 PM this evening to 1 AM EST
     Sunday for WVZ001>004-012-021-509>514.

&&

$$

SYNOPSIS...22
NEAR TERM...22
SHORT TERM...22/Milcarek
LONG TERM...MLB/Milcarek
AVIATION...MLB